MEASUREMENT OF CP VIOLATION PARAMETER USING RARE KAON DECAYS

衰减KL→π^<0>νν是测量CP违和参数的最佳衰减之一。为了寻找灵敏度最高的衰变，我们准备了KEK E391a实验，并于2004年2月开始运行。该实验也将作为下一个实验测量其分支比的先导实验。采用蒙特卡罗模拟方法研究了J-PARC 50GeV质子加速器的新实验。我们发现，通过利用衰减区域的一侧作为量热计，接受度增加了4倍。当加速器的设计强度为10%时，我们可以观测到150个信号事件，并以6%的精度测量CP违和参数。我们还研制了一种能测量光子入射角的新型量热计。这是一个串状探测器，每个纤维读取三个不同深度区域中的一个。在SPring8上使用1.5-2.8GeV光子的测试实验表明，它的角度分辨率为9%/ Sqrt （E (GeV)）。我们还开发了一种新型光导，将光纤中的光以较浅的入射角注入光管。使用光导后，光电子的数量增加了1.8倍。我们还发表了Fermilab KTeV实验的结果，包括CP破坏参数ε′/ε的测量，建立了直接CP破坏。

The decay KL→π^<0>νν is one of the best decays to measure the CP violation parameter.We prepared experiment KEK E391a to search for the decay with the best sensitivity, and started running in February 2004. The experiment will also serve as a pilot experiment for the next experiment to measure its branching ratio.We studied a new experiment for J-PARC 50GeV proton accelerator using Monte Carlo simulation. We found that the acceptance is increased by a factor 4 by utilizing the side of the decay region as a calorimeter. With the 10% of the design intensity of the accelerator, we can observe 150 signal events and measure the CP violation parameter with a 6% accuracy.We also developed a new calorimeter which can measure the incident angle of photons. This is a shashlik type detector with individual fibers reading one of the 3 different depth regions. A test experiment using 1.5-2.8GeV photons at SPring8 showed that it has an angle resolution of 9%/ Sqrt (E (GeV) ). The resolution can be improved further by increasing the light yield etc..We also developed a new type of light guide to inject the light from fibers to a phototube at a shallow incident angle. Using the light guide, the number of photoelectrons was increased by a factor 1.8.We also published results from Fermilab KTeV experiment, including the measurement of CP violation parameter, ε'/ε, establishing the direct CP violation.